U.S. patent number 8,749,337 [Application Number 13/422,082] was granted by the patent office on 2014-06-10 for micro coil apparatus and manufacturing methods therefor.
This patent grant is currently assigned to Maradin Technologies Ltd.. The grantee listed for this patent is Adi Baram, Inbal Herer, Sharon Hornstein, Matan Naftali, Menashe Yehiel. Invention is credited to Adi Baram, Inbal Herer, Sharon Hornstein, Matan Naftali, Menashe Yehiel.
United States Patent |
8,749,337 |
Baram , et al. |
June 10, 2014 |
Micro coil apparatus and manufacturing methods therefor
Abstract
A method for manufacturing a conductive coil, the method
comprising using a semiconductor fabrication process (e.g. TSV) to
manufacture a coil, typically a planar spiral conductive coil.
Inventors: |
Baram; Adi (Yoqneam,
IL), Naftali; Matan (Moshav Aloney-Aba,
IL), Hornstein; Sharon (Pardes Hanna, IL),
Herer; Inbal (Kibbutz Ramat Hashofet, IL), Yehiel;
Menashe (Moshav Yogev, IL) |
Applicant: |
Name |
City |
State |
Country |
Type |
Baram; Adi
Naftali; Matan
Hornstein; Sharon
Herer; Inbal
Yehiel; Menashe |
Yoqneam
Moshav Aloney-Aba
Pardes Hanna
Kibbutz Ramat Hashofet
Moshav Yogev |
N/A
N/A
N/A
N/A
N/A |
IL
IL
IL
IL
IL |
|
|
Assignee: |
Maradin Technologies Ltd.
(Yoqneam, IL)
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Family
ID: |
43033446 |
Appl.
No.: |
13/422,082 |
Filed: |
March 16, 2012 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20120235779 A1 |
Sep 20, 2012 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCT/IL2010/000570 |
Jul 15, 2010 |
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61242813 |
Sep 16, 2009 |
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Current U.S.
Class: |
336/200; 336/184;
336/182; 336/205; 336/223 |
Current CPC
Class: |
H01L
21/76898 (20130101); H01F 5/003 (20130101); H01F
41/041 (20130101); H01F 2007/068 (20130101); H01F
2017/002 (20130101); H01L 2924/0002 (20130101); H01L
23/5227 (20130101); Y10T 29/49071 (20150115); H01L
2924/0002 (20130101); H01L 2924/00 (20130101) |
Current International
Class: |
H01F
5/00 (20060101); H01F 27/28 (20060101); H01F
27/30 (20060101) |
Field of
Search: |
;336/200,205,223,184,182,198 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2005036567 |
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Apr 2005 |
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WO |
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2008072248 |
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Jun 2008 |
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WO |
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Other References
Sitaram R Arkalgud et al., "Leading Edge 3D Technology for High
Volume Manufacturing" in VLSI Tech.Dig.,2009, p. 68-69. cited by
applicant .
K-W Lee et al., "3D Heterogeneous Opto-Electronic Integration
Technology for System-on-Silicon (SOS)" in IEDM Tech. Dig., 2009,
p. 531-534. cited by applicant .
Wei-Chung Lo et al., "TSV and 3D Wafer Bonding Technologies for
Advanced Stacking System and Application at ITRI" in IEDM Tech.
Dig., 2009, p. 70-71 (22.2.1-22.2.4). cited by applicant .
D. Y. Chen et al. "Enabling 3D-IC foundry technologies for 28 nm
node and beyond: through-silicon-via integration with high
throughput die-to-wafer stacking" in IEDM Tech. Dig., 2009, p.
353-356 (14.3.1-14.3.4). cited by applicant .
J. H. Klootwijk et al., "Ultrahigh Capacitance Density for Multiple
ALD-Grown MIM Capacitor Stacks in 3-D Silicon" in IEEE EDL 2008
vol. 29, p. 740-742. cited by applicant .
Mitsumasa Koyanagi., "New 3D Integration Technology and 3D System
LSIs" in VLSI Tech. Dig. 2009, p. 64-67. cited by applicant .
H.Y. Li et al Ultra-Compact Micro Coil via Multi-Layers Stacking of
Dense TSV Coils for MEMS Application, Jan. 25, 2012. cited by
applicant .
Guerin Louis et al.,"High aspect ratio planar coils embedded in SU8
photoepoxy for MEMs applications", vol. XII, No. 1, Sep. 13, 1998,
pp. 11-14, XP008115449. cited by applicant.
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Primary Examiner: Talpalatski; Alexander
Assistant Examiner: Hossain; Kazi
Attorney, Agent or Firm: Browdy and Neimark, PLLC
Claims
The invention claimed is:
1. An electric coil device comprising: a spiral comprising a
plurality of electro-conductive turns and an isolation layer
between the turns, the isolation layer comprising a spiral trench
of varying width formed of a surrounding electrically isolating
bulk, the electro-conductive turns comprising an electro-conductive
material at least partly filling said spiral trench; and connection
feeds in and out of the spiral, wherein the spiral is generally
planar defining a coil plane and wherein the feeds extend both
upward and downward from said coil plane, and wherein the trench
which varies in height includes a peripheral portion, an
intermediate portion and a central portion and wherein the
cross-sectional height of the intermediate portion is greater than
the cross-sectional heights, e.g. common cross-sectional height if
equal, of the peripheral and central portions.
2. A device according to claim 1 in which the bulk is formed of one
of the following group of materials: Silicon, Pyrex, Polymer.
3. Electronic circuitry apparatus including a coil device according
to claim 1.
4. Electronic circuitry apparatus according to claim 3 which
includes a plurality of coils and is operative to induce
electromagnetic flux coupling.
5. Multi-level electrical coil apparatus comprising a stack of
electrically connected electric coil devices according to claim
1.
6. Apparatus according to claim 4 which comprises an
electromagnetic actuator.
7. A device according to claim 1 wherein the trench which varies in
height includes a peripheral portion, an intermediate portion and a
central portion and wherein the cross-sectional height of the
intermediate portion is greater than the cross-sectional heights,
e.g. common cross-sectional height if equal, of the peripheral and
central portions.
8. Apparatus according to claim 5 wherein the spiral in each
electric coil device has top and bottom main surfaces and defines a
hollow portion at its center extending through the top and bottom
main surfaces such that the stack has a hollow center comprising a
concatenation of the hollow portions of each of the electric coil
devices as stacked.
9. Apparatus according to claim 8 and also comprising a
ferromagnetic structure residing in the hollow center of the stack
and extending along a plurality of the electric coil devices in the
spiral.
10. A device according to claim 1 wherein a plurality of connecting
points are provided on at least one of the upper surface of the
trench and the lower surface thereof, thereby providing diverse
options for connectivity.
11. A device according to claim 1 wherein connecting points are
provided at both ends of the trench on both the upper and lower
surfaces of the trench, thereby providing diverse options for
connectivity.
12. Apparatus according to claim 9 which includes electrical
connection apparatus between the stack and an electrical circuit,
thereby to generate an actuator.
13. An electric coil device comprising: a generally planar spiral
defining a coil plane and comprising a plurality of
electro-conductive turns and an isolation layer between the turns,
the isolation layer comprising a spiral trench of varying width
formed of an electrically isolating material, the
electro-conductive turns comprising an electro-conductive material
at least partly filling said spiral trench; and connection feeds in
and out of the spiral which extend both upward and downward from
said coil plane, wherein the spiral in each electric coil device
has top and bottom main surfaces and defines a hollow portion at
its center extending through the top and bottom main surfaces such
that the stack has a hollow center comprising a concatenation of
the hollow portions of each of the electric coil devices as
stacked.
14. Multi-level electrical coil apparatus comprising a stack of
electrically connected electric coil devices according to claim
1.
15. Apparatus according to claim 13 and also comprising a
ferromagnetic structure residing in the hollow center of the stack
and extending along a plurality of the electric coil devices in the
spiral.
16. A device according to claim 1 wherein a plurality of connecting
points are provided on at least one of the upper surface of the
trench and the lower surface thereof, thereby providing diverse
options for connectivity.
17. A device according to claim 1 wherein connecting points are
provided at both ends of the trench on both the upper and lower
surfaces of the trench, thereby providing diverse options for
connectivity.
18. Apparatus according to claim 15 which includes electrical
connection apparatus between the stack and an electrical circuit,
thereby to generate an actuator.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a continuation-in-part of PCT Application No.
PCT/IL2010/000570, entitled "Micro coil apparatus and manufacturing
methods therefor," the entire contents of which are hereby
incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to the field of
micro-electro-mechanical systems (MEMS) and to micro-coil
apparatus.
BACKGROUND OF THE INVENTION
State of the art micro-coil apparatus and related technologies are
described in the following publications and documents: 1. U.S. Pat.
No. 5,724,015 to Tai et al. 2. U.S. Pat. No. 6,535,098 to Yeo et
al. 3. U.S. Pat. No. 6,493,861 to Li et al. 4. U.S. Pat. No.
4,818,966 to Miyamoto et al. 5. U.S. Pat. No. 5,711,912 to
Chatterjee et al. 6. U.S. Pat. No. 5,610,433 to Merrill et al. 7.
U.S. Pat. No. 5,912,608 to Asada. 8. U.S. Pat. No. 6,171,886 to
Ghosh et al 9. U.S. Pat. No. 5,543,956 to Nakagawa et al 10.
Published PCT Application WO/2008/072248 to Ramot 11. US Patent
Application 2005275497 to Ramadan et al. 12. US Patent Application
2009001510 to Matz et al. 13. Published PCT Application
WO/2005/036567 to White et al. 14. U.S. Pat. No. 5,583,474 to
Mizoguchi et al. 15. US Patent Application 2009/0102059 to Ishii et
al. 16. PCT Patent Application No. PCT/IL2008/000743 "Gimbaled
scanning micro-mirror apparatus" was published on Dec. 10,
2009.
Since image sensor production has been achieved using TSV
technology, more and more TSV technology development and
demonstration of different function block integration are reported,
e.g. in: Sitaram R Arkalgud et al., in VLSI Tech. Dig., 2009, p. 68
K-W Lee et al., in IEDM Tech. Dig., 2009, p. 531. Wei-Chung Lo et
al., in IEDM Tech. Dig., 2009, p. 70 3D interconnects by the Cu TSV
are described in D. Y. Chen et al., in IEDM Tech. Dig., 2009, p.
353. TSV technology can be designed as a functional device. For
example, J. H. Klootwijk et al., in IEEE EDL 2008 Vol. 29, p. 740,
reported TSV designed at ultra-high capacitance density. Another
important application of TSV technology is the integration of
different functional devices e.g. as described in Mitsumasa
Koyanagi, in VLSI Tech. Dig. 2009, p. 64.
The disclosures of all publications and patent documents mentioned
in the specification, and of the publications and patent documents
cited therein directly or indirectly, are hereby incorporated by
reference.
SUMMARY OF CERTAIN EMBODIMENTS OF THE INVENTION
Many applications employ coils as electronic devices. In
particular, there are applications with the need of very small
coils (i.e., micro-coils) to be operated as electrical inducers for
various electrical circuits or as part of very small
electro-magneto apparatuses. One such application is a coil for the
inductance of magnetic flux for a MEMS micro-electro-magneto
actuator.
Electro-magneto actuators offer numerous advantages in realizing
micro-actuators for many applications. Their high force-density,
resulting in a device that can operate in extreme conditions, along
with their linear electro-mechanical response and small size, is
advantageous in many applications. In such applications, coils may
be critical components as they determine the magnetic flux and
inductance of the actuator results in an operating regime.
There is thus provided, in accordance with certain embodiments of
the present invention, an electric coil device comprising a spiral
comprising a plurality of electro-conductive turns and an isolation
layer between the turns, the isolation layer comprising a spiral
trench formed of a surrounding electrically isolating bulk, the
electro-conductive turns comprising an electro-conductive material
at least partly filling the spiral trench; and Connection feeds in
and out of the spiral.
Further in accordance with certain embodiments of the present
invention, the bulk is formed of one of the following group of
materials: Silicon, Pyrex, and Polymer.
Also provided, in accordance with certain embodiments of the
present invention, is electronic circuitry apparatus including a
coil device as described above.
Further provided, in accordance with certain embodiments of the
present invention, is electronic circuitry apparatus as described
above which includes a plurality of coils and is operative to
induce electromagnetic flux coupling.
Further provided, in accordance with certain embodiments of the
present invention, is multi-level electrical coil apparatus
comprising a stack of electrically connected electric coil devices
as described above.
Yet further provided, in accordance with certain embodiments of the
present invention, is a method for manufacturing an electric coil
device, the method comprising providing a spiral comprising a
plurality of electro-conductive turns and an isolation layer
between the turns, including forming the isolation layer by forming
a spiral trench of a surrounding electrically isolating bulk, and
forming the electro-conductive turns by at least partly filling the
spiral trench with an electro-conductive material; and providing
connection feeds in and out of the spiral.
Further in accordance with certain embodiments of the present
invention, the spiral trench is formed by micromachining the
bulk.
Still further in accordance with certain embodiments of the present
invention, the apparatus also comprises isolated electrical feeds
between the layers which are formed by micro-machining.
Additionally in accordance with certain embodiments of the present
invention, an air gap which is generally parallel to the turns, is
provided in the conductive material.
Further in accordance with certain embodiments of the present
invention, the connection feeds are formed by Through Silicon Via
(TSV) technology.
Still further in accordance with certain embodiments of the present
invention, the trench is completely filled with the
electro-conductive material.
Further in accordance with certain embodiments of the present
invention, a BGA (ball grid array) process is used to connect the
coil devices.
Still further in accordance with certain embodiments of the present
invention, the method also uses a Silicon etch process to form the
spiral trench.
Additionally in accordance with certain embodiments of the present
invention, the bulk comprises bulk Silicon patterned using deep Si
etch according to at least one spiral geometry specification, the
turns are isolated, the coils are metallized; and in and out
connection feeds are patterned at two ends of the spiral.
Further in accordance with certain embodiments of the present
invention, the connection feeds are formed by micromachining.
Still further in accordance with certain embodiments of the present
invention, the coils are metallized using a seed layer process, an
electroplating process and a front side polishing process.
Additionally in accordance with certain embodiments of the present
invention, at least one step uses a semiconductor fabrication
process.
Further in accordance with certain embodiments of the present
invention, at least one step uses a TSV semiconductor fabrication
process.
Still further in accordance with certain embodiments of the present
invention, the spiral geometry specification includes at least one
of the following characteristics of the spiral: cross-section of
each turn, number of turns, and pitch.
Yet further in accordance with certain embodiments of the present
invention, the trench has spiral walls and the air gap is provided
by deposition of the conductive material only adjacent the spiral
walls rather than in the entirety of the trench.
Still further in accordance with certain embodiments of the present
invention, the spiral has a central head end and a peripheral tail
end and wherein the using includes fabricating at least one
electrical connector by generating at least one through-silicon via
for the spiral.
Additionally in accordance with certain embodiments of the present
invention, the method also comprises using the semiconductor
fabrication process to manufacture a second planar spiral
conductive coil thereby to define at least first and second
through-silicon vias for the first and second coils respectively,
and using the vias to electrically connect the head end of the
first coil to the tail end of the second coil.
Further in accordance with certain embodiments of the present
invention, the semiconductor fabrication process is used to
manufacture a first plurality of clockwise spiral conductive coils
and a second plurality of counterclockwise spiral conductive coils
thereby to define through-silicon vias for the coils, and using the
vias to at least once electrically connect a head end of an
individual one of the first plurality of clockwise coils to an end
of an individual one of the second plurality of counterclockwise
coils and to connect the head end of the individual one of the
second plurality of counterclockwise coils to an end of another
individual one of the first plurality of clockwise coils and to
generate a stack of conductive coils in which each pair of adjacent
coils includes a clockwise coil and a counter-clockwise coil.
Further in accordance with certain embodiments of the present
invention, the method also comprises connecting at least one
through-silicon via to a controlling electronic circuit.
Still further in accordance with certain embodiments of the present
invention, the coil comprises trenches defined in a bulk and
wherein the trenches are at least 40 microns deep
Additionally in accordance with certain embodiments of the present
invention, the spiral trench has spiral walls and wherein providing
a spiral comprises extending effective coil length by manufacturing
a pair of intertwined spiral conductive coils, wherein the trench
has a trench cross-sectional width and the walls are coated with
first and second conductive coatings respectively which are
together thinner than the trench cross-sectional width thereby to
form a non-conductive gap between the conductive coatings so as to
define the intertwined spiral conductive coils.
Further in accordance with certain embodiments of the present
invention, the apparatus comprises an electromagnetic actuator.
Still further in accordance with certain embodiments of the present
invention, the connection feeds are patterned using Front side
passivation thereby to generate a front passivation layer, Opening
of a contact in the front passivation layer, Wafer
polishing/etching, Back side passivation thereby to generate a back
passivation layer, and Opening a contact in the back passivation
layer.
Further in accordance with certain embodiments of the present
invention, the spiral comprises a planar spiral.
Still further in accordance with certain embodiments of the present
invention, the coating of the walls is effected by an
electroplating process.
The turns of the spiral planar coil provided herein may be round
e.g. generally circular but may also be of any other suitable shape
such as oblong which may include straight line segments.
In accordance with still other embodiments of the present
invention, the coil comprises trenches defined in a bulk and the
trenches are at least 5 microns deep and are up to 1000 microns
deep. The depth of the trench is dependent on the thickness of the
bulk, which conventionally varies up to 1000 microns. However, this
depends on the manufacturing process used hence is not intended to
be limiting.
According to some embodiments, the trench varies in at least one of
cross-sectional width and cross-sectional height (the terms
"height" and "depth" are used herein generally simultaneously). For
example, it may be the case that the trench varies in height and
includes a peripheral end portion, an intermediate portion and a
central end portion adjacent the spiral's center point, and the
cross-sectional height of the intermediate portion differs from the
cross-sectional heights, or common cross-sectional height if equal,
of the peripheral and central portions.
Typically, the aspect ratio along the trench varies e.g. from 1:1
or 2:1 to 5:1, where aspect ratio is defined as the ratio of trench
cross-sectional height to width.
A particular advantage of certain embodiments is that the intensity
of the electro-magnetic flux is increased due to providing a core
extending along the entire length of a stack of connected coils.
Such a long core is capable of housing a relatively long hence
massive ferromagnetic body generating electro-magnetic flux. The
electro-magnetic force/moment resulting from this structure is thus
enhanced, being an increasing function of the mass of the
ferromagnetic body. Simultaneously, according to certain
embodiments, the foot-print remains small since the spirals or
coils are stacked vertically rather than being positioned side by
side. Typically, the number of spirals in the stack is anywhere
from 1 to 20 or more, depending how much electromagnetic flux is
required for the application.
It is appreciated that coils may be connected to one another either
in parallel or in series.
The connection feeds are typically formed such that each coil has
at least one first connection feed in the upper surface of the
substrate and at least one second connection feed at the bottom
surface of the substrate. A particular advantage is that the
connection of the coil to a voltage source can be selectably
effected from either of the coil's upper or lower surfaces.
Example: The widths of each of the portions that comprise the
trench may be as follows: 10-50 microns width for the peripheral
portion, 5-100 microns for the intermediate portion and 10-50
microns for the central portion. The height of these portions may
be determined by the aspect-ratio. For example, given a 1:1 aspect
ratio, the heights may be: 10-50 microns for both the peripheral
and the central portions, and 5-100 microns height for the
intermediate portion. For a 5:1 aspect ratio, the heights may be:
50-250 microns for both the peripheral and the central portions,
and 25-500 microns for the intermediate portion. For a 10:1 aspect
ratio, the heights may be: 100-500 microns for both the peripheral
and the central portions, and 50-1000 microns for the intermediate
portion. It is appreciated that higher aspect ratios are possible
and may be used to create different dimensions of the trenches.
The ratio between the peripheral and central portions to the
intermediate portion may be selected dependent on the aspect ratio
used to create these portions and/or on the application that the
coil is designed for. For applications that employ intensive
electro-magnetic flux, the length of the intermediate portion of
the coil may be much larger than the coil's two end portions (its
peripheral and central portions). In this case, the ratio may be
taken to an extreme of peripheral length and central length <1%
and the intermediate length >99% from the entire length.
However, for applications where the intensity of the flux is of
least importance, and/or where the foot-print of each coil should
be as small as possible, and when stacking of coils is used to
enhance the overall flux, then the ratio may be changed to the
other extreme, say peripheral and central lengths may be 15% each
and the intermediate length may be 70%.
The metal filling process is typically determined by the
application and/or the manufacturing process. The width of the
metal layer may be 1 micron or even less or may entirely fill the
trench width. So, if a 10 micron width is used, and the metal fill
is 1 micron (at each side of the trench), an 8 micron air gap is
created. For wider trenches the air gap may be much higher. Also,
if the metal filling is thicker, say 4 microns width, an air gap of
2 microns is created.
According to some embodiments, some or all of the above parameters
may be controlled to a considerable extent or absolutely such that
all of the above values are merely exemplary.
In accordance with an embodiment of the presently disclosed subject
matter, there is provided a device wherein the trench which varies
in height includes a peripheral portion, an intermediate portion
and a central portion and wherein the cross-sectional height of the
intermediate portion is greater than the cross-sectional heights,
e.g. common cross-sectional height if equal, of the peripheral and
central portions.
In accordance with an embodiment of the presently disclosed subject
matter, there is further provided a method wherein the providing a
spiral comprises providing a single photolithography mask including
a spiral having a peripheral portion, an intermediate portion and a
central portion each having a cross-sectional width and wherein the
cross-sectional width of the intermediate portion is greater than
the cross-sectional widths of at least one of the peripheral and
central portions.
In accordance with an embodiment of the presently disclosed subject
matter, there is yet further provided a method comprising bounding
at least one relatively shallow portion of the spiral trench at its
bottom by a substrate and generating a through-hole from at least
one relatively deep portion, defining a depth, of the spiral by
filling the entire depth of the relatively deep portion of the
spiral trench with metal.
In accordance with an embodiment of the presently disclosed subject
matter, there is yet further provided an apparatus wherein the
spiral in each electric coil device has top and bottom main
surfaces and defines a hollow portion at its center extending
through the top and bottom main surfaces such that the stack has a
hollow center comprising a concatenation of the hollow portions of
each of the electric coil devices as stacked.
In accordance with an embodiment of the presently disclosed subject
matter, there is yet further provided an apparatus comprising a
ferromagnetic structure residing in the hollow center of the stack
and extending along a plurality of the electric coil devices in the
spiral.
In accordance with an embodiment of the presently disclosed subject
matter, there is yet further provided a method wherein the
cross-sectional width of the intermediate portion is greater than
the cross-sectional widths of both of the peripheral and central
portions.
In accordance with an embodiment of the presently disclosed subject
matter, there is yet further provided a method wherein the
cross-sectional widths of the peripheral and central portions are
equal.
In accordance with an embodiment of the presently disclosed subject
matter, there is yet further provided a device wherein a plurality
of connecting points are provided on at least one of the upper
surface of the trench and the lower surface thereof, thereby
providing diverse options for connectivity.
In accordance with an embodiment of the presently disclosed subject
matter, there is yet further provided a device wherein connecting
points are provided at both ends of the trench on both the upper
and lower surfaces of the trench, thereby providing diverse options
for connectivity.
In accordance with an embodiment of the presently disclosed subject
matter, there is yet further provided an apparatus which includes
electrical connection apparatus between the stack and an electrical
circuit, thereby to generate an actuator.
In accordance with an embodiment of the presently disclosed subject
matter, there is yet further provided a method wherein the spiral
is formed by a spiral fabrication process and wherein BGA (ball
grid array) is used to connect a plurality of coil devices each
formed by the spiral fabrication process and wherein said BGA is
formed integrally within the spiral fabrication process rather than
by a separate fabrication process.
In accordance with an embodiment of the presently disclosed subject
matter, there is yet further provided a method comprising using at
least one of the peripheral and central portions as a connection
feed to at least one of a voltage source and a circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
Certain embodiments of the invention are illustrated in the
following drawings:
FIG. 1 is a simplified cross-sectional view of a prior art
electromagnetic actuator;
FIGS. 2A-2B, taken together, form a simplified flow diagram of
steps of a method for fabricating Through Silicon Via (TSV) coils
according to certain embodiments of the present invention.
FIG. 2C is a key to FIGS. 2A-2B.
FIG. 3 is a simplified flowchart illustration of a general method
for manufacturing an electric coil device operative according to
certain embodiments of the present invention;
FIG. 4 is a simplified cross-sectional view of a coil structure
with 4 layers of coils constructed and operative according to
certain embodiments of the present invention;
FIG. 5 is a simplified cross-sectional view of a coil structure
with a double turn design constructed and operative according to
certain embodiments of the present invention.
FIGS. 6-8 are respective isometric cut-away, cross-sectional and
top view illustrations of an electric coil device constructed and
operative in accordance with certain embodiments of the present
invention.
FIG. 9 is a simplified top view illustration of a spiral 710
comprising a plurality of electro-conductive turns 720 and an
isolation layer 730 between the turns, the isolation layer being
fabricated by forming a spiral trench of a surrounding electrically
isolating bulk, and forming the electro-conductive turns by only
partly filling the spiral trench with an electro-conductive
material, thereby to form a spiral air gap 740 as shown.
FIG. 10 is a simplified isometric illustration of a stack of coils
including a first plurality of clockwise spiral conductive coils
and a second plurality of counterclockwise spiral conductive coils
wherein each pair of adjacent coils includes a clockwise coil and a
counter-clockwise coil.
FIGS. 11A and 11B are top view simplified illustrations of
respectively clockwise and counterclockwise spiral conductive
coils, constructed and operative in accordance with certain
embodiments of the present invention.
FIGS. 12A-12B are side view illustrations of BGA (ball grid array)
process-formed connectors used to connect a coil device in a stack
to a coil below it and above it, respectively, in the stack.
FIGS. 13-17 are useful in understanding example methods for dense
TSV coil process development and 8 TSV coil stacking for MEMs
applications which methods are operative according to certain
embodiments of the present invention, in particular:
FIG. 13 is a graph of current and magnetic field change with
applied voltage.
FIG. 14 is a graph of modification of current and magnetic field
with time under 1.679 volts.
FIG. 15 is a graph of Inductance performance with frequency of 8
stacking coils.
FIG. 16 is a table of Coil resistances of wafer level after
front-side (Under Bump Metallization) UBM patterning.
FIG. 17 is a table of resistance values for 4 example coils.
FIGS. 18A-18B, taken together, form a simplified flow diagram of a
process flow for fabricating Through Silicon Via (TSV) coils, using
bulk Silicon, Glass or SoG (Silicon on Glass), or any other
substrate material that is suitable for TSV technology as the
surrounding substance of the coil.
FIG. 18C is a key to FIGS. 18A-18B.
FIG. 18D is a top view of a substrate formed of a bulk
material.
FIG. 18E is a key for the top view and sectional illustrations of
FIG. 18D.
FIG. 19A is a perspective illustration of an example spiral trench
constructed and operative in accordance with certain embodiments of
the present invention.
FIGS. 19B and 19C are respective perspective illustrations
depicting various electrical connections, in schematic form,
between stacked coils defining a counterclockwise and clockwise
current direction, respectively, all in accordance with certain
embodiments of the present invention.
FIGS. 20A-20B, taken together, illustrate stages of a generally
self-explanatory process for generating a stack of coils so as to
provide flux to e.g. so as to drive an axis in a mechanical device,
all in accordance with certain embodiments of the present
invention.
FIG. 20C is a key for FIG. 20B.
FIG. 21 is a simplified cross-sectional view of an example
electromagnetic actuator constructed and operative according to
certain embodiments of the present invention.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THE INVENTION
Reference is made to FIG. 1 (Prior art), which illustrates a
typical prior art electromagnetic actuation mechanism in
cross-section. The electromagnetic actuator comprises a stator
(i.e., non-rotating portion) and a rotor pivoting about an axis 30
along a route having a length of less than several dozen microns,
the rotor comprising a flexure element fixedly associated with the
stator, the flexure element comprising a magnetic portion 40; the
stator comprising a Ferro-magnetic core 50 having a curved
configuration which is almost closed thereby to define an air-gap
60 closing the curved configuration and having a width exceeding
the route length by only a few microns and a conductive coil 70
wrapped around at least a portion of the almost closed curved
configuration of the Ferro-magnetic core 50. At least the magnetic
portion 40 of the flexure element is disposed within the air-gap
60, thereby to generate a first magnetic field in the air-gap 60
and an alternating current flows through the conductive coil 70
thereby to generate a second, alternating magnetic field within the
air gap 60, the magnetic fields being indicated by arrows 75. The
magnetic portion 40 is oriented such that the first magnetic field
generated thereby in the air-gap 60, when interacting with the
second, alternating magnetic field within the air-gap, generates a
movement about the axis 30.
The conductive coil 70 of the electromagnetic actuator of prior art
FIG. 1 induces electromagnetic flux, as indicated by arrows 85,
which is typically directed by a flux director 90 and which drives
the actuator.
The general model of the electromagnetic circuit can be deduced by
Ampere law as an equilibrium of the applied electromagnetic force
(on the left hand side) and the induced magnetic flux multiplied by
the circuit reluctance (right hand side). F=Ni=.phi.(t) (1) where N
is the number of coil turns and i is the applied current. The
dissipative power of the operation of the motor can be described
by: P=iV=i.sup.2R.sub.coil (2) where R is the coil impedance that
can be computed as:
.rho..times..times. ##EQU00001## where L.sub.c is the coil length,
A.sub.c is the coil cross-section area and .rho. is the coil
specific density. Hence the length of the coil is a function of the
coil number of turns, estimating the length of each turn as a
circumferential of a circle; the resistivity of a coil with N turns
may be expressed as:
.rho..times..times..apprxeq..rho..times..times..times..times..pi..functio-
n..rho..pi..times..times..function..times..times..times.
##EQU00002## and the overall power, per one layer of coil, with
initial radius of r0 and pitch p as:
.times..rho..times..times..pi..times..times..function..times..times.
##EQU00003##
A prevalent method of making coil devices is by turning a
conductive wire. An alternative method is by utilizing well known
semiconductors compatible with processing of thin film. By using
such processes for manufacturing coils, the cost of such devices
can be reduced; better electromagnetic response and reliability can
be achieved along with a simplified assembly process for other
components, such as for electromagnetic actuators, as is known in
the art. In current state-of-the-art fabrication methods for
creation of such coils, thin layers are utilized for the creation
of metal strips (the coil itself) and the surrounding substance
material in which the coil is fabricated (usually, a passivation
layer). The design of the coil is limited by this fabrication
process e.g., thickness of metal cross-section is limited by the
deposition thickness of the isolation layer (passivation layer
e.g.).
However, in some applications, there is a need for high currents,
low resistance and high inductance. In order to achieve these, a
larger cross section of the coil is needed along with an increasing
number of coil turns. This is not achieved in current
state-of-the-art semiconductor thin layer compatible manufacturing
techniques.
According to certain embodiments of the present invention, bulk
micro-machining technology is used to create such coils, in various
bulks, whose bulks may for example be formed of Silicon, Pyrex, or
suitable polymers. In particular, Through Silicon Via (TSV)
technology is utilized in a manner compatible with semiconductor
processes. TSV realizes electrical contacts from one side of wafers
to the other. The conductive contacts may be realized either (a) by
using through wafer patterning (e.g., deep Silicon etch, or laser
drilling) and filling with electroplated or deposited metal or
conductive material (e.g., doped Poly-Silicon), or (b) by realizing
a through via and covering the side walls with a conformal
conductive layer.
In TSV processes the bulk material of the wafer is utilized as the
surrounding substance of the coil, along with via making processes
(e.g., TSV technology) to pattern the coils, allowing wire
cross-section to be increased to desired parameters, and the coils
to be engineered accordingly.
The conventional TSV process employs a temporary support wafer
which is temporarily bonded to the processed wafer and de-bonded,
after the process is completed, for further treatment such as
dicing, packaging and assembly.
A fabrication process for TSV coils in accordance with certain
embodiments of the present invention is now described with
reference to FIGS. 2A-2B which, taken together, form a simplified
flow diagram of a process flow for fabricating Through Silicon Via
(TSV) coils, using bulk Silicon, e.g., as the surrounding substance
of the coil. The third, rightmost column of FIGS. 2A-2B provides
illustrations of the outcome of each stage in the process flow. The
fabrication process typically includes some or all of the following
stages and steps, suitably ordered e.g. as shown:
aa. Step 310--Initially, the surrounding substance material is
patterned using deep Si etch, according to coil specifications such
as but not limited to metal cross-section, number of turns, and
pitch.
bb. Subsequently, in step 320, turns are isolated.
cc. Metallization of the coils (steps 330 to 350).
dd. In steps 360 to 400, connection feeds to the coil are patterned
on both sides of the coil (in and out connections).
Steps 310-410 are now described in detail:
310: Performing deep Si etch
320: Passivation of the etched trenches
330: Seed layer process
340: Electroplating
350: Front side CMP
360: Front side passivation
370: Open contact in the passivation layer
380: Wafer polish/etch
390: Back side passivation
400: Open contact in the passivation layer
410: BGA process
FIG. 2C is a key for the flow diagram of FIGS. 2A-2B.
FIG. 3 is a simplified flowchart illustration of a general method
for manufacturing an electric coil device operative according to
certain embodiments of the present invention.
In order to increase the number of turns, multiple structures of
coils can be assembled one on top of the other as illustrated in
FIG. 4 which is a simplified cross-sectional view of a coil
structure with 4 (say) layers of coils. Alternatively or in
addition, an air gap can be provided in the middle of the
conductive material's cross-section, so as to provide additional
turns which are intertwined in one another, e.g. as shown in FIG. 5
which is a simplified cross-sectional view of a coil structure with
double turns design which uses the same notation (e.g. for air and
silicon) as FIG. 4.
Referring again to FIG. 3, the method for manufacturing an electric
coil device according to certain embodiments of the present
invention may include some or all of the following steps, suitably
ordered e.g. as follows:
Step 510: forming a spiral trench, typically at least 40 microns
deep, of a surrounding electrically isolating bulk e.g. by
micromachining the bulk or using a silicon etch, e.g., to achieve a
predetermined typically planar spiral geometry specification
typically including at least one of the following characteristics:
cross-section of each turn, number of turns, and pitch.
Step 520: forming electro-conductive turns by partly or fully
filling the spiral trench with an electro-conductive material (if
material is deposited only adjacent the spiral walls, e.g. by
electroplating, an air gap which is generally parallel to the turns
is provided in the conductive material).
Step 530: providing connection feeds in and out of the spiral e.g.
using TSV technology or micromachining.
Step 540: optionally, fabricating other coils using the above
steps, stacking them, e.g. using a BGA (ball grid array) process to
connect the coils being stacked as shown in FIGS. 12A-12B, and
providing isolated electrical feeds between the layers e.g. by
micro-machining such that the head end of each coil is electrically
connected to the tail end of an adjacent coil and each pair of
adjacent coils includes a clockwise coil and a counter-clockwise
coil.
Step 550: optionally, connecting at least one connection feed to a
controlling electronic circuit e.g. so as to generate an
actuator.
FIGS. 6-8 are simplified respective isometric cut-away,
cross-sectional and top view illustrations of an electric coil
device constructed and operative in accordance with certain
embodiments of the present invention and including a spiral 610
comprising a plurality of electro-conductive turns 620 and an
isolation layer 630 between the turns, the isolation layer
comprising a spiral trench formed of a surrounding electrically
isolating bulk 640, the electro-conductive turns comprising an
electro-conductive material at least partly filling the spiral
trench; and connection feeds 650 in and out of the spiral. The
cross-sectional and cut-away views are cut along the axis
connecting the connection feeds in FIG. 8.
FIG. 9 is a simplified top view illustration of a spiral 710
comprising a plurality of electro-conductive turns 720 and an
isolation layer 730 between the turns, the isolation layer being
fabricated by forming a spiral trench of a surrounding electrically
isolating bulk, and forming the electro-conductive turns by only
partly filling the spiral trench with an electro-conductive
material, thereby to form a spiral air gap 740 as shown.
FIG. 10 is a simplified isometric illustration of a stack of coils
including a first plurality of clockwise spiral conductive coils
800, e.g. as shown in top view in FIG. 11A, and a second plurality
of counterclockwise spiral conductive coils 810, e.g. as shown in
top view in FIG. 11B, wherein each pair of adjacent coils includes
a clockwise coil and a counter-clockwise coil. Through-silicon vias
820 electrically connect an end, such as a head end 830 or tail end
840 (FIG. 11A) of each individual one of the first plurality of
clockwise coils to an end, typically the same end (head or tail) of
an individual one of the second plurality of counterclockwise coils
and connect the other end of the individual one of the first
plurality of clockwise coils to an end, typically the same end
(tail or head), of another individual one of the second plurality
of counterclockwise coils.
FIGS. 12A-12B are side view illustrations of BGA (ball grid array)
process-formed connectors 910 used to connect a coil device in a
stack to a coil below it and above it, respectively, in the stack.
Isolation material is denoted by reference numeral 920 and the
balls formed by the BGA process are denoted by reference numeral
930.
Example methods for dense TSV coil process development and 8 TSV
coil stacking for MEMs applications are now described in
detail.
In the illustrated example, a dense TSV coil and stacking process
suitable for MEMs applications is shown. The dense TSV coils (20 um
width, 10 um space, 90 um depth, in the illustrated example) are
void-free filled by Cu. 8 layer coil stacking is provided, using
conductive adhesive. The resistance, inductance, magnetic field,
and basic reliability of 8 dense coils stacking in the illustrated
example are described.
In the illustrated example, higher resistivity (30.about.40 Ohmcm)
substrates were used in the dense TSV coil process development for
the reduction of RF substrate loss in the MEMs application. The
full process included TSV coil process development, back side thin
wafer process, bonding and de-bonding for the dense TSV coil, laser
drilling for the center cavity formation and die stacking Dense TSV
coil is etched by the DRIE. Two step etching was applied for the
TSV coil and coil stacking connection.
Multiple DC plating steps were developed for the Cu void-free
plating in deep TSV trench. High polishing rate CuCMP process was
setup and applied in this development work. The coil performance in
the wafer level was tested after front-side UBM process by probe
station and HP 34401A multi-meter. The electric performance of the
coil is shown in the table of FIG. 16. Adhesive polymer is used for
the bonding of carrier wafer with TSV coil wafers after front side
UBM processing.
After back-grinding to 120 um and exposing back side coil contact
for the following on stacking, low temperature (150.degree. C.) SiN
was deposited and patterned at the passivation layer. Following the
back side UBM process, laser drilling was used for the formation of
the middle of the cavity. After de-bonding from EVG supporting and
dicing, conductive adhesive was used for 8 chip stacking, thereby
to generate a void-free Cu filling TSV coil.
The resistances of coils after 8 layer stacking are measured and
shown in FIG. 17. The measured resistances include contact
resistance and conductive adhesive resistance. The 8 coils stacking
resistance is matched with wafer level coil 0.9 Ohm. I-V
performance and magnetic field of 8 layer coil stacking were
measured using an Agilent E3631A Triple Out DC Power supply and a
475 DSP Gauss-meter. The distance between the magnetic field
detection and the 8 coil stacking center is around 2 mm. The
magnetic field and current changing with applied voltage are shown
in FIG. 13. The magnetic field of the 8 layer coils stacking
saturates from 4V. The linear I-V curve of 8 stacking coils is
shown in FIG. 13. The breakdown voltage of 8 stacking coils is 4.6V
from this coil measurement. This system was used to measure the
basic reliability performance of 8 layer stacking coils. 1.697V was
applied on the 8 stacking coils and the current and magnetic field
was measured with time. The measurement results are shown in FIG.
14. After 66 hours testing, the variation of current and magnetic
fields were .about.5-%, .about.10% respectively. The reliability of
8 dense TSV coil stacking was improved. Inductance is believed to
be an important factor for the 8 stacking coils. The inductance of
8 coils stacking is measured by 4285 A 75 KHZ-300 MHZ Precision LCR
Meter under 1V voltage. The variation of inductance with frequency
is shown in FIG. 15. The maximum value of 8 stacking coils
inductance is 389uH at 80 KHz. But inductance of 8 dense TSV coils
stacking reduces to .about.30 uH from 0.8 MHz to 1.3 MHz.
In the illustrated example of a dense TSV coil process with
void-free Cu filling, then, a thin wafer process is applied on the
back side of a dense TSV coil. Laser drilling is used for deep
cavity formation. An 8 dense TSV coils stacking functionality is
provided. The electric and magnetic fields of 8 stacking coils were
measured as described above. The 8 layer coils stacking can pass 66
hours electric stress testing under 0.19 A.
A fabrication process for TSV coils in accordance with certain
embodiments of the present invention is now described with
reference to FIGS. 18A-18B which, taken together, form a simplified
flow diagram of a process flow for fabricating Through Silicon Via
(TSV) coils, using bulk Silicon, Glass or SoG (Silicon on Glass),
or any other substrate material that is suitable for TSV technology
as the surrounding substance of the coil; the same materials may be
used for the process of FIGS. 2A-2B. The third, rightmost column of
FIGS. 18A-18B provide illustrations of the outcome of each stage in
the process flow. The method and of FIGS. 18A-18B and key of FIG.
18C may be as described above with reference to the method and key
of FIGS. 2A-2C, respectively, with corresponding reference numerals
indicating similar steps, except for the following differences:
Step 1310--as in FIGS. 2A-2B, initially, the surrounding substance
material is patterned using a suitable etch process, according to
coil specifications such as but not limited to metal cross-section,
number of turns, and pitch. However, different width dimensions of
the photolithography mask are used to yield varying depths for the
trench and a wide width results in a deeper trench. Here and in
step 310 of FIGS. 2A-2B, a deep Si etch, or RIE (Reactive Ion
Etch), or DRIE (Deep RIE), or a wet etch, or any other etch process
can be performed in order to create the vias.
In step 1340 (and in step 340 of FIGS. 2a-2b), optionally, an air
gap which is generally parallel to the turns is provided in the
conductive material by growing an electroplating layer on the
trench walls e.g. as shown in FIG. 9.
At step 1370 as well as at step 1400, optionally, UBM may be
applied for the fabrication.
Step 1410: The BGA process may be finished with a reflow.
FIGS. 18A-18B pertains to one example spiral coil, with particular
location of TSV (holes bound by BGA) i.e., from left to right,
deep, shallow, shallow, hole, deep, shallow, shallow. However, this
structure is of course merely exemplary. For example, the beginning
and/or end of the trench may be in different locations. For
example, given a mirror image with respect to the vertical axis, of
the cross-section shown in FIGS. 18A-18B, the beginning of the
trench may be on the right hand side of the trench.
Referring again to FIG. 3, it is appreciated that the spiral trench
may have any suitable depth, such as but not limited to 5 to 100
microns deep and may be generated e.g. by micromachining the bulk
or using or any etch process suitable for fabrication of the
vias.
The width of the spiral trench is typically not constant, typically
having a higher value e.g. of 10-50 microns at the peripheral and
central trench portions, and a lower value e.g. of 5-20 microns
along the intermediate portion disposed between the peripheral and
central trench portions. The varying width of the trench yields a
varying aspect-ratio for the trench cross section. During the DRIE
process, the depth of the trench in the substrate bulk is
determined from the width of the photolithography mask.
Consequently, a wide width results in a deeper trench. The
difference of the trench depths can be defined by considering,
inter alia, the cross section's aspect ratio (AR). The AR along the
narrow part of the trench is 5/1 while the AR in the edges of the
trench is less than 2/1.
Usually, in MEMS designs, structures with different dimensions and
aspect ratios coexist on a single microchip. When the structures
that are formed inside the bulk material are deep (e.g. a depth of
several microns, say 10-100 microns deep), the process is called "a
deep silicon etching process". As opposed to other etching methods,
this process generates `slots` in the material whose depth greatly
exceeds their width. The ratio between the trench's depth and its
width, i.e. its aspect ratio, is greater than 1 for deep silicone
etching processes. In the deep etching process an ARDE (aspect
ratio dependent etching) effect is known. For features with
different dimensions etched simultaneously, the ARDE effect causes
larger features to be etched faster. Therefore, time is also
typically a factor taken into consideration when determining a mask
width suitable for a desired structure depth.
After the DRIE phase, a metal layer is filled inside the trench
e.g. using a conventional electroplating process. Finally, when the
bottom side of the substrate is polished/etched, the deep trench is
exposed such that these edges, that are now filled with metal,
enable a transition of conductivity between the top and bottom
layers of the substrate, and hence vertical stacking of coils is
possible.
The connection feeds are typically formed such that each coil has a
first connection feed in the upper surface of the substrate and a
second connection feed at the bottom surface of the substrate. This
design enables connection of an array of coils in a vertical
structure e.g. stack, comprising as many layers as required. The
electrical connection of the stacked-coils structure is such that
one end of the electrical connection is attached to the stack's top
surface and the other end of the electrical connection is attached
to the stack's bottom surface.
The fabrication process of the connection pads may comprise a
conventional UBM process and may include some or all of the
following operations: After the passivation layer on the upper
surface of the substrate, open contacts are effected at specific
locations on the passivation layer. Then, metal layers (e.g.
Aluminum, Gold, Titanium, Nickel but not limited to these specific
materials) are dissipated at these locations, so as to form the
connection pads. This process is typically performed separately
from the fabrication process of the trench so as to be less
complicated.
Connecting between two (or more) UBM pads that belong to different
substrates may be effected by applying solder material using
suitable technologies such as, but not limited to BGA or Metal
evaporation, typically on top of the UBM layer. Connection between
these layers may be effected by positioning two (or more)
substrates, one on top of the other, and by means such as, e.g. by
applying force or using a reflow process.
Solder bumps are typically formed at a preliminary step in the
fabrication process of the coils, and may be used for
interconnecting layers of a semiconductor device. According to
certain embodiments, solder bumps are fabricated at four locations
of the coil (two in the top layer and another two in the bottom
layer) as shown (the four spherical elements in FIG. 18D). However,
according to other embodiments, depending on the application, the
type of connection (in series or in parallel), and other possible
factors, solder bumps may be formed at other locations and/or at
less than all of the above locations e.g. in the embodiment of FIG.
20 which requires only two connections, one in the upper layer and
another in the bottom layer.
The design and fabrication process of the coils typically comprises
creating a hollow aperture in the center of the coil, and enabling
insertion of a ferromagnetic material for the creation of an
electro-magnetic force, by means of an electromagnetic flux.
Electromagnetic flux is increased, advantageously, by more
ferromagnetic material being placed in the coil center, e.g. by
placing a ferromagnetic body which extends throughout the
substrate.
FIG. 18D is a top view of a substrate formed of a bulk material,
with a spiral trench revolving around a central core and, below the
top view, a cross-sectional illustration taken along the line A-A,
of the spiral trench. The spiral trench may be formed by the method
of FIGS. 18A-18B. Shallow and narrow, medium, and deep and wide
trench portions are shown, having widths and heights of W1 and H1,
W2 and H2, and W3 and H3, respectively. Typically at least one end
of the spiral trench, such as the peripheral or central end
thereof, or both as in the illustrated embodiment so as to enhance
the number of connection possibilities, is/are deeper (hence wider)
than the centrally located portion.
As shown, the trench includes a centrally located portion which is
wide and long/high enough (W3, H3) to serve as a portion of the
hollow core, in which a ferromagnetic body may reside. The hollow
core typically extends the length (perpendicularly to the plane of
the page) due to the centrally located trench portion being long
enough (H3) to adjoin other hollow core portions of H3 length which
may be formed by other spirals stacked under or over the spiral of
FIG. 18D thereby to form a single hollow core extending along the
entire length of the stack. Portions of width W2 and length/height
H2 are typically wide enough hence long enough to serve as vias.
W2, H2 may equal or be somewhat less than W3, H3 respectively.
Portions of width W1 and/height H1 are narrow hence short enough to
preserve insulation (e.g. due to intervening silicon) between
similar layers of substrate above and below them.
EXAMPLE
W1=20, W2=50, W3=250, H1=110, H2=120, H3=130,
FIG. 18E is a key for the top view and sectional illustrations of
FIG. 18D.
The ratio between the intermediate portion to the beginning and end
portions may vary as required, and may for example be 99% and 1%,
or 70% and 30%.
According to certain embodiments, the connection of a coil or stack
to a voltage source and/or circuit can be effected from either its
upper or lower surfaces (top and bottom coils respectively),
providing versatility. For example:
FIG. 19A is a perspective illustration of an example spiral trench
constructed and operative in accordance with certain embodiments.
Elements denoted A, B, C, D denote the connecting points of the
coil, typically with associated BGA "balls". In the illustrated
embodiment two connecting points are provided on the upper surface
of the trench and two on the lower surface, providing diverse
options for connectivity e.g. as described in FIGS. 19B-19C.
Connections may then be provided so as to suit the desired current
direction and other aspects of the application.
FIGS. 19B and 19C are respective perspective illustrations
depicting various electrical connections, in schematic form,
between stacked coils defining a counterclockwise and clockwise
current direction, respectively.
In FIG. 19B, the three coils are stacked such that the current
direction is counter-clockwise. The upper coil is connected to the
current source through point B. Point C at the upper coil is
connected to point A of the middle coil. Point D in the middle coil
is connected to point B of the bottom coil. Point C of the middle
coil is connected to the remainder of the electrical circuit. It is
appreciated that alternatively, the current source may be connected
to point A of the upper coil, yielding a clockwise current
direction. In this case, the connection between the coils may be as
follows: Point D of the upper coil connected to the middle coil at
point B; middle coil connected at point C to the bottom coil at
point A; point D of the bottom coil connected to the remainder of
the electrical circuit.
FIG. 19C depicts stacking of three coils such that the current
direction is clockwise. The upper coil is connected to the current
source through point B. Point C at the upper coil is connected to
point A of the middle coil. Point D in the middle coil is connected
to the point B of the bottom coil. Point C at the bottom coil is
connected to the remaining electrical circuit.
FIGS. 20A-20B, taken together, illustrate a generally
self-explanatory process for generating a stack of coils so as to
provide flux to e.g. so as to drive an axis in a mechanical
device.
Regarding step 1305, the mask width is selected to achieve the
required depth, as is known in the art, based inter alia on the
material being etched, time for the process, the material used for
the etching, and many more. Etching rate dependency on aspect ratio
is described, for example, in Gottscho, Jurgensen and Vitkavage,
"Possible mechanisms for aspect ratio dependent etching rates", J.
Vac Sci Technol B, 10, 2133 (1992).
Regarding step 1420, the number of coils to be stacked is
determined per application. The required energy or force or torque
for a particular application is known and one can be computed from
the other as is known in the art. From the required energy and the
input current, the required inductance of the inductor (coil) is
found. When coils are connected in series, the equivalent
inductance is known to be the sum of the individual coil's
inductances such that the number of coils which need to be stacked
may be determined, given the application.
FIG. 21 is a simplified cross-sectional view of an example
electromagnetic actuator constructed and operative according to
certain embodiments. As opposed to the prior art electromagnetic
actuator of FIG. 1, the ferromagnetic material 50 of FIG. 1 is
replaced by a narrow U-shaped ferromagnetic element 55. For
example, the diameter of the ferromagnetic material may be 200-500
microns, or higher or lower (but typically not below 5 microns)
depending on the intensity of the magnetic flux.
A coil structure 75 may for example comprise a pair of 4-floor
(say) stack of coils, which together form a common cut-through hole
about their central axes within which the arms of the U-shaped
ferromagnetic element 55 may reside. The stacked-coils are
typically threaded on the ferromagnetic material. Connection
between the coils and the electrical circuit may be performed using
BGA 95 which may be formed in an integral part of the production
process of the coils. It is appreciated that a particular advantage
of the embodiment of FIG. 21 is its small foot-print. The coils are
connected in series but are located one on top of the other;
consequently, the foot-print is small.
The applicability of the invention includes but is not limited to
devices which are manufactured based at least partly on
semiconductor processes, and applications that use induction to
produce an electro-magnetic field, including moveable components or
other components that use an electromagnetic field for their
functionality. For example, miniature MEMS-based devices such as
but not limited to projectors, may be provided in which at least
one axis is driven by an Electro-Magnetic (EM) motor. The electric
circuit for the motor may include magnets, coil/s (also termed
herein "spirals") in which a ferromagnetic material resides and a
current source. The current that flows in the coils generates an
axis-driving magnetic field, due to the presence of the
ferromagnetic material. Certain embodiments of the present
invention may be used to generate the coil/s or "spirals" in which
the ferromagnetic material resides.
According to an embodiment of the present invention, only one metal
line is connected to the device, whereas an output metal wire is
connected at the bottom side. A `cut-through` hole (TSV) goes from
the top to the bottom surface of the matrix, e.g. as shown and
described herein, generating the driving circuit.
The height or depth of the device is typically indicative of the
number of layers of coils that are stacked, if the technology used
to generate the trenches imposes a technological limitation on the
depth of the trench. For example, if trenches can be no deeper then
100 microns whereas the device's thickness is more than, say,
100-150 microns, the device typically comprises more than one
layer.
It is appreciated that the coils need not be a separate stand-alone
component and may be part of a larger system. For example, as part
of designing of an Integrated-Circuit (IC), a spiral or coil as
shown and described herein may be utilized as a component in (say)
the top layer of the integrated circuit, whereas other components,
located at other layers of the silicone, may or may not be as shown
and described herein.
Any dimensions stipulated herein are merely by way of example. For
example, IC designs may be a few orders of magnitude smaller than
the dimensions specifically stipulated herein. For example, the
thickness of a, say, metal layer in IC technology is .about.1800
Angstrem whereas the dimensions stipulated herein assume a metal
layer which may be about 100-120 microns thick.
Features of the present invention which are described in the
context of separate embodiments may also be provided in combination
in a single embodiment. Conversely, features of the invention,
including method steps, which are described for brevity in the
context of a single embodiment or in a certain order may be
provided separately or in any suitable subcombination or in a
different order. "e.g." is used herein in the sense of a specific
example which is not intended to be limiting. It is appreciated
that in the description and drawings shown and described herein,
functionalities described or illustrated as systems and sub-units
thereof can also be provided as methods and steps therewithin, and
functionalities described or illustrated as methods and steps
therewithin can also be provided as systems and sub-units thereof.
The scale used to illustrate various elements in the drawings is
merely exemplary and/or appropriate for clarity of presentation and
is not intended to be limiting.
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